Getting this short:

Can current flow from a powered USB hub's power adapter (lying 10 Meter away) back to computer via usb port and cause damage to Computer components like mobo, etc? What should be my concerns?

Using a 2 Amp 5V Power adapter to power a 10m Long Active Repeater USB extension cable with 4 port HUB & plugging into PC's Front port, causes the following, after PC is shut down (bit scary)

  • PC Chassis fan to keep running (thought slower than regular speed)
  • Front Chassis HDD & power LED to turn on (though bit dim)
  • may be other things which i cant detect/see at chip level, in motherboard??

More detail (in case U want to ask):

To run 4 High power (needing >450 mAmps) Wifi Adapters, far away from PC, Bought Active Repeater USB Extension Cable with 4 Ports & power port at far end http://www.ebay.com/itm/33FT-USB-2-0-Male-to-Female-Extension-Cable-Hub-Splitter-Adapter-with-4-USB-Port-/390846115254 (see 2nd picture for single pin adapter port on it) & Powered it by plugging it with locally bought (medium quality) 2 Amp 240V AC to 5V DC Power Adapter

Even 4 Wifi Adapters run fine (appear to) using this setup, but running chassis fan, dimly lighted Power & HDD LED, even when PC is switched off is bit scary & surely mean 5V & some current is flowing all though that 10 meter extension cable into my USB port & powering stuff.

Can this cause damage? and what should be my concerns. Of course I can't switch off the power adapter (lying 10 meters away from PC) every time I switch off my PC to prevent this.




Yes, in theory. My hunch is yes also in practice.

I've personally experienced both motherboard damage from back power from a misbehaving USB device.

Power where power is not expected can definitely cause issues.

It should be noted that I don't entirely understand how you have everything hooked up. But if power is going into the computer backwards I would consider that cause for concern.

  • Thanks but 1)Can you explain "Overpower"? 2)Given that power adapter is supplying 5V only,which is normally available in USB port & amount of current flow only depends upon how much an electronic parts needs, why should it damage it? (other than the fact that it is surely causing wear & tear of chassis fan (& other electronic components, which i can't detect, if so) & more electricity bill).....Saying so, i would like to inform that i detected this after about 20 hrs which includes hour of PC being turned off (when that Current/voltage was kind of reverse flowing). PC remains fine till date. – SuperUserMan Jun 7 '14 at 18:25
  • couple more 3)What can be at fault here for allowing current to flow backward, if so? A)Repeater cable cum hub B) Power adapter.........I just added picture of Setup too in 1st post.Thanks – SuperUserMan Jun 7 '14 at 18:41
  • Overpower meaning higher voltage than expected. In the event of (for instance) a short in a device. – OmnipotentEntity Jun 7 '14 at 18:44
  • @OmnipotentEntity A short circuit by itself does not change the voltage. It might however lead to a higher current than designed for, depending on some other things. – a CVn Jun 7 '14 at 18:48
  • While USB ports in specific are designed to accept 5V power, because power is leaking from the USB Hub i have concerns about the quality of the hub, and whether or not it may short seriously in the future. It should be noted that it already should absolutely not be doing what it's doing right now. Which means that you're probably already exceeding the capacity of the hub, which increases the chance of a power related failure situation. – OmnipotentEntity Jun 7 '14 at 18:48

I have (Had) the same problem when powering a USB hub from its own psu, in that it powers the PC when the PC is powered down, I had tried 3 different hubs and all do the same. The easiest way to stop this is to cut the red + wire on the USB cable that goes from inside the hub to the PC. You could fit a switch or fit a blocking diode, (I just cut the red wire, just means the hub will have to be powered to work properly) My 2 hub's was connected and powered for weeks,back feeding 2 PC and none had any problems at all before I cut the + wire.


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